Process for producing silicon steel sheet having (100) plane in the rolling plane



Aug. 16, 1966 Filed Dec. 23, 1963 magnetic torque 5 SheetsSheet 1 By Saforu Taguchi Akira Sakakura Hiroshi Takechi Hironon' Takashima Aug. 16, 1966 SATORU TAGUCHI ETAL 3,

PROCESS FOR PRODUCING SILICON STEEL SHEET HAVING (100) PLANE IN THE ROLLING PLANE Filed Dec. 25, 1963 5 Sheets-Sheet 2 FIG.3 (0) FIG.3 (b) INVENTORS By Soforu Taguchi Akira Sakakura Hiroshl Takechi Hi ronori Takashima g- 1966 SATORU TAGUCHI ETAL 3,266,955

PROCESS FOR PRODUCING SILICON STEEL SHEET HAVING (100) PLANE IN THE ROLLING PLANE Filed Dec. 25, 1963 5 Sheets-Sheet 5 INVENTORS By Saforu Taguchi Akira Sakakura Hiroshi Takechi Hiranori Takashima 6, 1966 SATORU TAGUCHI ETAL. 3,266,955

PROCESS FOR PRODUCING SILICON STEEL SHEET HAVING (100) PLANE IN THE ROLLING PLANE Filed Dec. 23, 1963 5 SheetsSheet 4 Fl6.5 (a) RD INVENTORS By Soforu'Taquchi Akira Sakakura Hiroshi Takechi Hironori Takashima Aug. 16, 1966 Filed Dec. 25, 1963 percentage of appearame of (100K000 orienfufion in the produci SATORU TAGUCHI ETAL 3,266,955 PROCESS FOR PRODUCING SILICON STEEL SHEET HAVING 100) PLANE IN THE ROLLING PLANE 5 Sheets-Sheet 00:0 0020 0030 0.0400000 0.060 0.010 002300.090 0:00 0710 ouzo also 014 also ingof C INVENTORS 8y Saforu Taguchi Akira Sakokura Hiroshi Takechi Hironori Takashimo United States Patent 3,266,955 PROCES FOR PRODUCING SILICON STEEL SHEET HAVING (109) PLANE IN THE ROLL- ING PLANE Satoru Taguehi, Akira Sakakura, Hiroshi Takechi, and Hironori Talrashima, Kitakyushu, Japan, assignors to Yawata Iron & Steel Co. Ltd., Tokyo, Japan Filed Dec. 23, 1963, Ser. No. 332,423 Claims priority, application Japan, Dec. 28, 1962, 37/ 59,376 1 Claim. (Cl. 148-111) This invention relates to a process for producing silicon steel sheet. More particularly, the present invention relates to a process for producing silicon steel sheet or strip having (100) plane in the rolling plane of the sheet.

Silicon steel sheet is widely used as soft magnetic materials for iron cores of transformers and generators. As well known silicon steel has a cubic lattice texture, in which there are three easy magnetization directions vertical to one another and has an advantage of the least energy being required for magnetizing the silicon steel core when a magnetic field is applied in parallel with such directions. Due to this advantage various attempts have been heretofore made in controlling the crystal orientation of the silicon steel sheet in accordance with its object of use.

In the case of a single-oriented silicon steel sheet, in which the easy magnetization axis is parallel with the rolling direction, magnetic induction and other magnetic characteristics of very high value may be obtained in the rolling direction but not in the other directions on the rolling plane. On the other hand, in the case of a doubleoriented silicon steel sheet, in which the easy magnetization axis is parallel to both the rolling direction and the direction at a right angle thereto, magnetic induction and other magnetic characteristics are equally high in both of the above mentioned directions. Therefore, when punching iron cores for use in a largesized rotor from the double-oriented silicon steel sheet, iron cores of higher magnetizability may be obtained than punching them from the single-oriented silicon steel sheet. Moreover, iron cores made of the double-oriented silicon steel may be lighter in weight than those made of the single-oriented silicon steel sheet. However, iron cores made of the double-oriented silicon steel sheet are not suited for a small-sized rotor, because there occurs a striking deviation between the magnetic flux passing direction and the easy magnetization direction in some part of the iron core. For that reason the non-directional oriented silicon steel sheet has been usually used to make iron cores for smallsized rotors in order to eliminate the above said devia tion.

However, it is technically very diflicult to produce a double-oriented silicon steel sheet, which has (100) plane in the rolling plane and moreover highly directional permeability in both the rolling direction and the direction at a right angle thereto, and also a non-directional oriented silicon steel sheet which has also (100) plane in the rolling plane and in which the magnetic characteristics show substantially no difference in any direction on the rolling plane and further the permeability is high in all directions on the rolling plane. In general, the production of a silicon steel sheet in which the 100) plane appears in the rolling plane has not been successful by means of the ordinary metallurgical processes.

The object of the present invention is to provide a process of producingsilicon steel sheets, in which the (100) plane appears in the rolling plane, by means of an easily operative metallurgical technique, or as a typical form thereof, a double-oriented silicon steel possessing such excellent magnetic characteristics as adapted for 3,266,955 Patented August 16, 1966 making iron cores for use in a large-sized rotor or a plane non-directional oriented silicon steel sheet particularly adapted for making iron cores for use in a smallsized rotor.

Another object of the present invention is to provide a process of producing a double-oriented silicon steel sheet having (100) plane in the rolling plane or a nondirectional oriented silicon steel sheet having (100) plane by regulating the ratio of recrystallization grains having 100) [001] orientation to recrystallization grains having 100) [011] orientation.

Other objects of the present invention will be made clear by referring to the following description and the accompanying drawings.

FIGURE 1 shows diagrams showing the crystal orientation and easy magnetization direction of crystal grains forming oriented silicon steel sheets of the following three types (the silicon steel sheet so designated hereinafter shall include steel strip), that is, a single-oriented silicon steel sheet (a), a double-oriented silicon steel sheet (b) and a Wassermann-oriented silicon steel sheet (c).

FIGURE 2 shows diagrams showing magnetic torque curves of (100) [001] orientation, (100) [011] orientation and a resultant of them.

FIGURE 3 shows a pole figure (a) showing the crystal orientation of a hot-rolled steel sheet, which has been crosswise hot-rolled, and a {110} pole figure (b) showing the crystal orientation of a hot-rolled steel sheet, which has been hot-rolled in a single direction.

FIGURE 4 shows {110} pole figures showing the respective crystal orientations of primary recrystallization grains obtained by cold-rolling and sequentially annealing the hot-rolled silicon steel sheet, which has been crosswise hot-rolled (a) and the hot-rolled silicon steel sheet, which has been hot-rolled in a single direction (b).

FIGURE 5 shows (100) pole figures showing the respective crystal orientations of secondary recrystallization grains and microsketches showing the respective crystal structures of secondary recrystallization grains thereof obtained by further annealing the primary recrystallization grains of two kinds as of the hot-rolled steel sheets (a) and (b) as shown in FIGURE 4.

FIGURE 6 is a diagram showing the ratios of the (100) [001] orientation to (100) [011] orientation appearing in the products of the present invention in response to the variation of carbon content of an ingot used as the starting material.

As well known, in a unit lattice of any iron silicon alloy the edge of the lattice, that is, the 100 orientation is the easiest to magnetize and then the direction of the diagonal of the lattice plane or the 110 direction is the next easiest to ,magnetize and the most difiicult to magnetize is the direction of the cubic diagonal of the lattice or the lll direction. The designations of the planes and directions here mentioned are shown in the notation of Millers indices. The detailed description of the definitions may be found, for example, on pages 1 to 25 of Structure of Metals, second edition, written by C. S. Barrent and published by McGraw-Hill Co., New York, 1952.

It was the single-oriented silicon steel sheet that first fulfilled the requirement to apply a magnetic field in parallel with the easy magnetization direction. This is formed of crystal grains having such crystal orientation as shown in FIGURE 1(a) and is crystallographically designated as (110) [001] orientation, in which the easy magnetization axis is parallel with the rolling direction. Accordingly, the single-oriented silicon steel is characterized by the magnetic induction and other magnetic characteristics being excellent in the rolling direction, but low in another direction in the rolling plane, for instance, in the direction at a right angle to the rolling direction, because the ll axis appears in the latter direction, and the lowest in the 1ll direction.

The present invention is to provide a process of producing so-called (100) plane silicon steel sheets having no 1l1 axis, which is the most difficult to magnetize, in the rolling plane. A preferred example thereof is the double-oriented silicon steel sheet which is formed of crystal grains having such crystal orientation as is shown in FIGURE 1(b) and is crystallographically designated as (100) [001] orientation, and in which the easy magnetization axis is parallel with the two directions as of the rolling direction and the direction at a right angle thereto. Accordingly, the double-oriented silicon steel sheet is charactertized by that the magnetic induction and other magnetic characteristics are excellent in both of the above mentioned two directions and that the 1ll axis does not appear in the rolling plane. FIGURE 1(a) shows a kind of the double-oriented silicon steel sheet known as a silicon steel sheet of Wassermann-orientation, which is designated crystallographically as (100) [011] orientation. The double-oriented silicon steel sheet of Wasserrnannorientation is characterized in that the easy magnetization axis 100 appears in direction 45 degrees from the rolling direction and at a right angle thereto. The 1ll axis does not also appear in the rolling plane.

As already mentioned, the double-oriented silicon steel sheet which is a preferred product of the present invention is suited for making iron cores for use in a largesized rotor, but not in a small-sized one. For the latter purpose non-directional oriented silicon steel sheet is used, which is also a preferred object of the present invention and is characterized in having a (100) plane in the rolling plane and having grains of (100) [00L] orientation and those of (100) [011 orientation in the same ratio. It is desirable that the permability is made both high and substantially equal in all directions in the plane of the silicon steel sheet, when punching iron cores for use in a smallsized rotor. The silicon steel sheet of random crystal orientation heretofore used for iron cores for use in a small-sized rotor was defective in that its permeability was low, though substantially equal in all directions in the plane of the sheet. On the contrary, the non-directional oriented silicon steel sheet obtained by the present invention fulfills the requirements that the permeability should be both high and substantially equal in all directions in the plane.

In FIGURE 2, which shows magnetic torque curves, FIG. 2(a) is a magnetic torque curve of (100) [001] orientation, FIG. 2(b) that of (100) [011] orientation and FIG. 2(0) is when two aforesaid curves are overlapped one over the other. As seen from the last figure, these two curves cancel each other when they are overlapped, as the four ridges or peaks of each orientation no longer appear, and the sheet becomes non-directional oriented. That is to say, if there are equivalents of recrystallization grains of (100) [001] orientation and recrystallization grains of (100) [011] orientation in the sheet plane, the sheet becomes uniformly non-directional oriented and has only the (100) plane in the sheet plane, thereby rendering it ideal for making iron cores for use in a smallsized rotor. Besides, even in the cases where recrystallization grains of (100) [001] orientation and recrystallization grains of (100) [011] orientation are existing at any ratio, the lll axis of bad magnetizability will not appear in the rolling plane and its permeability is superior to any silicon steel sheet of random orientation, heretofore used for iron cores of a small-sized rotor.

Usually the magnetizability of the double-oriented silicon steel sheet is expressed by B which means a magnetic induction in gausses at 10 oersteds, while the magnetizability of the non-directional oriented silicon steel sheet is expressed by B in lieu of B which means a magnetic induction in gausses at 25 oersteds. It is selfevident that the more the easy magnetization axis 100 of each crystal grain forming the double-oriented silicon steel sheet is arranged in the rolling direction or the direction at a right angle thereto, the higher the magnetizability of the steel sheet will be. In other words, the higher the value of B the better the magnetizability of the steel sheet. A double-oriented silicon steel sheet showing a B value of 19,000 gausses in both the rolling direction and the direction at a right angle thereto may be said to be substantially ideal as a silicon steel sheet containing about 3% Si for making iron cores for use in a large-sized rotor. In the case of the non-directional oriented silicon steel, in which there should be no difference in magnetic characteristics in all directions in the rolling plane, a B value of 16,000 gausses will be sufiicient to meet the properties required for iron cores for use in a small-sized rotor.

Concerning the processes of producing silicon steel sheets having specifically selected orientations the following methods are known: (1) The method of producing a single-oriented silicon steel sheet, in which the silicon steel sheet is hot-rolled in a single direction and then the thus hot-rolled sheet is cold-rolled in the hot-rolling direction and sequently the cold-rolled sheet is subjected to an annealing in a non-specified atmosphere, thereby the recrystallization grains of the orientation, crystallographically designated as (110) [001] orientation, which is known as G oss texture," is produced. (2) The method of producing a double-oriented silicon steel sheet, in which the silicon steel sheet is hot-rolled in a single direction and then the hot-rolled steel sheet is crosswise cold-rolled and then the cold-rolled steel sheet is subjected to the annealing treatments, thereby to obtain the recrystallization grains of [001] orientation. Further, with respect to the method of producing a non-directional oriented silicon steel sheet, it .is known that a hot-rolled or a cast material is subjected to a substantial cold-rolling treatment followed by an annealing. The present invention relates to a novel method of producing the (100) plane silicon steel sheet on the basis of an entirely different idea from those of the conventional methods. That is, the present invention has succeeded in obtaining the (100) plane silicon steel sheet, more preferably the doubleoriented silicon steel sheet, which has 100% of recrystallization grains of substantial (100) [001] orientation, and the (100) plane non-directional oriented silicon steel sheet, which has 50% of recrystallization grains of (100) [001] orientation and 50 of recrystallization grains of (100) [011] orientation respectively, by means of the novel method, in which an ingot containing a small amount of Aland an amount of C regulated in accordance with the object of application, which is the starting material of the present invention, is first crosswise hot-rolled and then the thus obtained hot-rolled material is subjected to the conventional cold-rolling and annealing treatments. To put it briefly, the present invention is distinguished by the cross hot-rolling of the starting material from any conventional method, which is characterized by the step of hot-rolling in a single direction or cold-rolling and annealing treatments. The practical importance of the present invention resides in the conditions, in which the cross hot-rolling is carried out. In this novel process of the present invention it has been also discovered that the ratio of two component groups of recrystallization grains contained in silicon steel sheet to be obtained by the present invention-a group of recrystallization grains of substantial (100) [001] orientation and a group of recrystallization grains of substantial (100) [011] orientationdepends upon the carbon content of an ingot to be crosswise hot-rolled. Accordingly, the present invention has succeeded in obtaining the double-oriented silicon steel sheet having 100% of recrystallization grains of substantial (100) [001] orientation or the (100) non-directional oriented silicon steel sheet having 50% of recrystallization grains of substantial (100) [001] orientation and 50% of recrystallization grains of substantial (100) [011] orientation respectively by regulating the amount of carbon to be added to the ingot. Thus, the present invention has succeeded in obtaining the double-oriented silicon steel sheet and the non-directional oriented silicon steel sheet of any desired thickness and of excellent properties by subjecting the crosswise hot-rolled sheet to a conventional cold-rolling and annealing which may be carried out in a normal industrial atmosphere, for instance, in gas such as H N and Ar.

The cross hot-rolling of an ingot is used in the production of structural carbon steels or low alloy steels, but has never been applied to the production of silicon steel sheets. In the production of an oriented silicon steel the hotrolling of an ingot or slab is usually carried out only in' the longitudinal direction of the ingot and the thus obtained hot-rolled steel sheet is subjected to cold-rolling and annealing. In such case, the crystal orientation of the hot-rolled steel sheet belongs to a group of (X 1 I [011] orientation (wherein X is an arbitrary number), which makes the 011 axis parallel with the hot-rolling direction a rotating axis with the (100) [001] orientation as the center.

FIGURE 3(b) is the {110} pole figure showing the crystal orientation in the center part of the thickness of a hot strip of 3 mm. thick which has been prepared as follows: A ton-ingot of silicon steel sheet containing 3.0% Si, 0.04% C and 0.03% Al which has been made in an electric furnace and then cast, was bloomed in the longitudinal direction to make a slab of about 100 mm. thick and then the thus produced slab was soaked at a temperature of 1,250 C. for 30 minutes and subsequently hotrolled in the longitudinal direction to make the hot strip of 3 mm. thick. As seen from this figure, the crystal orientation after hot-rolled shows an excellent concentration of the (110) poles in the hot-rolling direction but a considerably dispersed concentration of the (110) poles in the direction at a right angle to the hot-rolling direction, demonstrating that this crystal orientation is a group of (X 1 1) [011] orientation with the (100) [011] orientation as the central orientation.

On the other hand, FIGURE 3(a) is the (110) pole figure showing the crystal orientation in the center part of the thickness of a hot strip of about 3 mm. thick which has been prepared as follows: A 500 kg.-ingot of silicon steel sheet containing 3% Si, 0.04% C and 0.03% A1, which has been made in an electric furnace and then cast, was bloomed in the longitudinal direction to make a slab about 90 mm. thick and then the thus obtained slab was soaked at a temperature of 1,280 C. for one hour and subsequently hot-rolled first in the direction at a right angle to the longitudinal direction of the slab at a re duction rate of about 70% so as to make an intermediate gauge slab of 27 mm. thick and secondly in the longitudinal direction of the first slab to make the hot strip of 3 mm. thick. As seen from FIGURE 3(a), the crystal orientation after crosswise hot-rolled shows a considerably similar degree of concentration of the {110} poles both in the last hot-rolling direction (in the direction of RD) and in the direction at a right angle thereto. The ratio thereof is 6.0X233X (wherein 1X is a random orientation intensity), considerably smaller than in the case of the hot-rolling in the single direction, in which the ratio of above 12X:4X is shown.

Next, the behaviors of the above mentioned two kinds of hot-rolled steel sheets, that is, the steel sheet which has been hot-rolled in a single direction and that which has been hot-rolled crosswise, after subjected to the sequent cold-rolling and annealing will be compared with each other.

FIGURES 4(a) and (b) are (110) pole figures in the center parts of the steel sheets after each of the above mentioned two kinds of hot-rolled steel sheets has been subjected to the following processes: At first each of them was annealed for 5 minutes in an H atmosphere containing 75% N by volume, the thus annealed steel sheet was pickled and then cold-rolled at the reduction rate of 65% so as to obtain a cold-rolled sheet of about 1 mm. thick and then the thus obtained cold-rolled sheet was annealed at a temperature of 800 C. for 5 minutes. As seen from these figures, the orientation of the primary recrystallization grains produced by the annealing carried out at a temperature of 800 C. for 5 minutes in the steel sheet hot-rolled in a single direction contains considerably (110) [001] orientation as shown in FIG. 4(b) while in the steel sheet hot-rolled crosswise the crystal orientation shows an octuple symmetry rotated by about 25 degrees around the 1 10 axis slightly deviated from the two hot-rolling directions as shown in FIG. 4(a).

FIGURES 5(a) and (b) are pole figures showing the orientations of recrystallization grains after the above two kinds of steel sheets already treated as above mentioned were further annealed in an atmosphere of 50% N +50% H by volume at a temperature of 1,200 C. for 20 minutes. As evident from these figures, recrystallization grains of substantial [001] orientation were produced in the case of single hot-rolling (FIGURE 5(b)) and recrystallization grains of substantial 100) [001] orientation were produced in the case of cross-hotrolling (FIGURE 5 (a) Further, in this process, the following interesting fact has been discovered by the inventors that even in carrying out exactly the same cold-rolling and annealing processes as mentioned above, when more than 0.050% C was contained in an ingot, recrystallization grains of (100) [011] orientation came to be mixed in after final annealing in response to the C content of the ingot.

FIGURE 6 shows the percentages of recrystallization grains of 100) [001] orientation and those of (100) [011] orientation forming a silicon steel sheet after being cold-rolled and annealed, varying in accordance with the change in percentage of C to be contained in the ingot. That is to say, depending on the percentage of C to :be contained in the ingot, grains of [001] orientation and those of [011] orientation are produced in the silicon steel sheet at percentages corresponding to the content of C of the ingot, though both grains have substantially the (100) plane in the rolling plane. Reversely speaking, by controlling the percentage of C to be contained in the ingot, the percentage of (100) [001] orientation and (100) [011] orientation of recrystallization grains after final annealing may be selected as desired, thereby the production of the (100) plane silicon steel sheets as mentioned in the introduction of this specification became possible.

In the method of producing the single-oriented silicon.

steel-sheet, in which the material is hot-rolled in a single direction and then the hot-rolled sheet is cold-rolled in one direction, recrystallization grains having (110) [001] orientation as shown in FIGURE 5( b) are produced, even if the carbon content of the material exceeds 0.05%. Further inthe method of producing the double-oriented silicon steel sheet having recrystallization grains of (100) [001] orientation, which has been discovered by the present inventors before the present invention and in which the hot-rolled silicon steel sheet is subjected to cross coldrolling, it has been confirmed that recrystallization grains of (100) [011] orientation did not appear, regardless of the carbon content of the ingot, provided that the hotrolling is carried'out only in a single direction. This indicates that the characteristics as shown in FIGURE 6, that is, the appearance of recrystallization grains of (100) [011] orientation in response to the carbon content of the ingot, is efiected only when the hot-rolling is carried out crosswise, and further is not at all influenced by how the sequent cold-rolling treatment would be carried out. In case of the hot-rolling in a single direction the carbon content of the ingot has no influence on determining the orientation of recrystallization grains after final annealing. In determining the orientation of recrystallization grains after final annealing it is very important to regulate the crystal orientation of the crosswise hot-rolled steel sheet. As it is, however, difiicult to designate the crystal orientation of the hot-rolled silicon steel sheet by the standard notation of Millers indices it should be regulated by the practical conditions of hot-rollings with a target of the ratio of the concentration degree of {110} poles in the direction of the final hot-rolling step and that in the direction at a right angle thereto. In order to obtain recrystallization grains of (100) [001] orientation and those of (100) [110] orientation it is necessary to keep the above mentioned ratio within a range of 4:1 to 1:4.

The silicon steel ingot used as the starting material in the present invention may be obtained by any of the ordinarily used steel making process, melting process and casting process. Further, the thickness of the hot-rolled sheet obtained by the cross hot-rolling is never to be limited. But, in view of the subsequent cold-rolling process, a too large thickness is disadvantageous and a too small thickness is not adapted to the capacity of the hot-rolling machine.

In working the present invention, the mos-t desirable thickness of the hot-rolled sheet before it is subjected to the cold-rolling treatment will be 1.0 to 7 mm. When carrying out a series of hot-rollings including the cross hot-rolling in the method according to the present invention the thickness of the hot-rolled sheet will reach 1 to 7 mm. Meanwhile, the cross hot-rolling may be carried out several times or the steel may be reheated. However, no matter how many times the cross hot-rolling may be carried out, the most important factors for assuring the successful result of the present invention are the conditions of hot-rollings in the last hot-rolling step and the penultimate hot-rolling step. The rolling step here designated means an operating step in which the steel is rolled in one direction, but not the number of passes of the steel through the rolls. The conditions for carrying out the cross hot-rolling according to the present invention are as follows:

(1) First of all, the cross hot-rolling should be carried out in directions forming a right angle :20 degrees .or preferably a substantially right angle with each other. If the angle made between the above two rolling directions is other than that, the ratio of the concentration degree of {110} poles in the direction of the final hot-rolling step to that in the direction at a right angle thereto will not come within a range of 4:1 to 1:4.

(2) The second condition is that the hot-rolling in the second last step should be carried out in the temperature range of 800 to 1,250 C. and should be accompanied by a reduction rate of more than 20% or preferably 30 to 93%.

(3) The third condition is that after the second last hot-rolling step is finished, the last hot-rolling step should be started by turning the direction of rolling and the hotrolling should be completed at least at a temperature of 600 C. The reduction rate of the thickness in the last hot-rolling should be at least 40% or preferably 40 to 97%. These second and third conditions are the factors particularly important to keep the ratio of the concentration degree of {110} poles in the direction of the final hot-rolling step to that in the direction at a right angle thereto within the range of 4:1 to 1:4. If the reduction rates of the thickness in the second last hot-rolling and the last hot-rolling are less than 20% and less than 40%, respectively, the ratio of the concentration degree of {110} poles in the direction of the final hot-rolling step to that in the direction at a right angle thereto will not come within the range of 4:1 to 1:4. Further, if carrying out the hot-rolling in the second last step at a temperature above 1,250 C. the concentration of {110} poles in this direction will not be effected. The reason why the hot-rolling in the second last hot-rolling step should not be carried out at a temperature below 800 C. arises from in reference to the temperature at which the last hot-rolling is to be carried out. That is to say, if the last hot-rolling is carried out below 600 C, {110} poles will be concentrated too much in this direction. Therefore, the last hot-rolling must be completed at a temperature above 600 C. In order to complete the hot-rolling at least at a temperature of 600 C. in the last hot-rolling step while effecting the reduction rate of the thickness above 40%, it is necessary to carry out the second last hot-rolling at a temperature above 800 C.

(4) Lastly, the fourth condition is that the steel should be heated at a temperature always lower than the temperature, at which the hot-rolling of said steel in the second last step has (been completed, in case it is necessary to reheat the steel which has been once cooled after the completion of the second last hot-rolling. If the steel is heated to a temperature higher than the temperature, at which the hot-rolling in the second last step has been completed, it will recrystallize and the concentration :of {110} poles in this direction will be completely lost.

It has been explained in FIGURE 3 that by force of the hot-rolling of silicon steel sheet {110} poles are concentrated in its rolling direction, and it has been discovered by the inventors that, in the hot-rolled sheet obtained by the cross hot-rolling carried out under the above mentioned conditions, the concentration degree of {110} poles in the final hot-rolling direction and that in the direction at a right angle thereto are similar to each other and that these similar concentration degrees of {110} poles in both directions are very favorable to obtain recrystallization grains having [001] and recrystallization grains having (100)[011] orientation after subjected to the sequent cold-rolling and annealing treatments.

In the silicon steel ingot used as the starting material in the present invention, there are added 2.0-4.0% Si, 0.010-0.060% acid soluble Al and C in the range of 0.010-0.l50%. But the addition of C is so selected Within the above mentioned range that recrystallization grains of (100)[001] orientation and recrystallization grains of substantial (100) [0 11] orientation may be produced at any desired mati-o after final annealing.

If C is less than 0.010%, recrystallization grains having a (100) plane parallel with the rolling plane will not be produced and, if the content of C is more than 0.15%, a greater labor will be required in decarburization thereof. Thus, C is limited to be within the range of 0.010-0.150%. The most desirable carbon content shall be described more in detail. In order to obtain the double-oriented silicon steel sheet of recrystallization grains of substantial (100)[001] orientation, C should be less than 0.05% as seen from FIGURE 6. On the contrary, in order to obtain the (100) plane non-directional oriented silicon steel sheet, in which equivalents of recrystallization grains of substantial (100) [001] orientation and recrystallization grains of a substantial (100)[011] orientation are mixed, C should be about 0.075%. If C is in a range of ODS-0.075%, the recrystallization grains of substantial (100)[001] orientation will \be more than 50%. Further, if C is more than 0.075%, recrystallization grains of substantial (100) [011] orientation will be more than 50% and the product will be no longer the perfect non-directional oriented silicon steel sheet. When C content is 0.075 the rate 1 of appearance of recrystallization grains of (100)[001] orientation centers at about 50%, scattering within the range of 40 to 60%. However, within this scattering range it is possible to restrain the difference between the maximum value and the minimum value of the magnetic induction B measured in the rolling plane to below 1000 gausses.

If Si is less than 2%, there will be caused a disadvantage of the increase in the iron core loss due to the low electric resistance of the product. If Si is more than 9 4%, the cold-rolling treatment will be diflicult due to brittleness. Therefore, Si is limited to 24%.

Al is added to form Al nitride, thereby to inhibit the growth of crystal grains of other orientations when producing recrystallization grains of substantial (100) [001] orientation and of substantial (100) [011] orientation. The content of soluble Al is defined to be in the range of 0.0l0.060%.

The other elements than Si, Al and C are substantially the same as those contained as impurities in an ingot in making an ordinary single-oriented silicon steel sheet. It is not necessary to specifically limit their contents. The balance is iron. Now, typical examples of ingot compositions, though the present invention is not to be thereby limited, are as follows:

(a) For use in the double-oriented silicon steel sheet having 100% of recrystallization grains of substantial (100)[001] orientation: 0.04% C, 3.0% Si, 0.10% Mn, 0.012% P, 0.025% S, 0.10% Cu, 0.020% lacid soluble A l, and 0.005% Ti, the balance being iron.

(b) For use in the non-directional oriented silicon steel sheet having 50% of recrystallization grains of substantial (100) [001] orientation and 50% of substantial (100) [011] orientation: 0.08% C, 3.0% Si, 0.09% Mn, 0.008% P, 0.020% S, 0.09% Cu, 0.030% acid-soluble Al, and 0.005% Ti, the balance being iron.

In the above explanation the conditions of ingot compositions and cross hot-rolling as are required to attain the object of the present invention are made clear. The hotrolled steel sheet obtained under the above mentioned conditions are further subject to the known cold-rolling and annealing treatments. A few embodiments of the cold-rolling and annealing treatments applied in the present invention will be explained in the following. In these embodiments it has been confirmed that the correlation between the carbon content of the ingot and the rate of appearance of recrystallization grains having (100) [001] orientation or of recrystallization grains having (100) [011] orientation has held true in any cold-rolling and annealing treatment. The conditions of sequent cold-rolling and annealing will be described in the following.

When the cold-rolling is carried out in a single direction, the reduction rate should be in the range of 50 to 80%. If it is less than 50% or more than 80%, recrystallization grains having (100) plane parallel with the rolling plane will not be produced after subjected to the sequent annealing. When the cold-rolling is carried out crosswise, the cold rolling may 'be carried out at the reduction rate of a wider range. If the reduction rate in the first coldrolling is 30 to 60%, the reduction rate in the cold-rolling in the crossing direction should be made in the range of 20 to 50%, and, if the reduction rate in the first coldrolling is 60 to 80%, the reduction rate in the crossing direction should be made in the range of 50 to 70%. In the combination of reduction rates in the cold-rolling outside this range, that is, in case either of the two reduction rates is too large or in case both of them are too small or too large, neither recrystallization grains of (100) [001] orientation nor (100) [011] orientation may 'be obtained. The crossing angle of the cross cold-rolling should be in the range of a right angle :20".

Whether it is the first cold-rolling in one direction or the second cold-rolling which is carried out in the crossing direction, it may be carried out at any angle with the final hot-rolling direction. However, it is rather preferable that the cold-rolling direction be 45 degrees with the final hot-rolling direction, when the production of recrystallization grains having (100) [001] orientation is intended, though any deviation in angle from 45 degrees will bring substantially no trouble on attaining the object. Particularly, when taking the production on an industrial scale into consideration, it is to recommend that either one of the cross cold-rolling and the final hot-rolling direction will coincide with each other.

The thus cold-rolled steel sheet is further subjected to the final high temperature annealing treatment. The temperature range of annealing is 1,000 to 1,300 C. When the temperature is below 1,000 C., recrystallization grains will not be completely produced. Further, annealing at a temperature above 1,300 C. is a condition more than is required. The atmosphere of annealing may be any kind of atmosphere, unless it contains such impurities as will extremely impair the magnetic characteristics as of the magnetic steel sheet. Usually, the most preferably used gas is H But, Ar and vacuum may be also applied.

The above mentioned high temperature annealing process may be commonly applied to obtain both of recrystallization grains having (100) [001] orientation and recrystallization grains having (100) [011] orientation. In case the steel sheet to be annealed contains so much carbon as to be thought to impede the production of recrystallization grains, the decarburization annealing should be carried out prior to the final annealing treatment. In such case, it is, however, not necessary to specify the carbon content after subjected to the said decarburization annealing, because the eifect of the carbon content of the ingot of determining the ratio of recrystallization grains having (100) [001] orientation and those having (100) [011] orientation after finally annealed will be exerted on up to the cold-rolling step, but not on the decarburization annealing which is carried out between the cold-rolling and the final annealing. Any decarburization annealing process adapted to the operating conditions may be selected from various known conventional ones. As there are so many kinds of the decarburization annealing conditions these need not be specified. However, for example, an atmosphere containing moisture and a temperature range of 750 to 1,000 C. may be recommended therefor.

By the above mentioned treatments the (100) plane magnetic silicon steel sheet of any thickness formed of recrystallization grains having substantial 100) [001] orientation and substantial (100) [011] orientation may be obtained. A particularly thin (100) plane silicon steel sheet may be obtained by repeating the above mentioned cold-rolling and annealing treatments.

Examples of the present invention shall be explained in the following:

Example 1 A 500 kg.-ingot made by melting in an electric furnace and containing 0.045% C, 3.02% Si and 0.035% acidsoluble Al was bloomed in its longitudinal direction to make a slab about 100 mm. thick. The sla-b was soaked at 1,250 C. for 30 minutes and was then hot-rolled at a reduction rate of about 70% in a direction at a right angle to the longitudinal direction of the slab to make an intermediate 30 mm. thick; At that time, the temperature of the slab was 1,100 C. Then this slab was turned by degrees in the direction and was hot-rolled by about 90% so as to be a hot-rolled sheet about 3 mm. thick. The finish temperature was 750 C.

The thus obtained hot-rolled sheet was annealed at 950 C. for 5 minutes. The annealed sheet was pickled and was then cold-rolling at a reduction rate of 64% in the same direction as of the final hot-rolling direction so as to be a cold-rolled sheet 1.08 mm. thick. The sheet was decarburized in wet hydrogen at 750 C. for 5 hours and was then annealed in an atmosphere of 50% N and 50% H at 1,200 C. for 20 hours, thereby recrystallization grains of [001] orientation have been produced.

The sheet was then cold-rolled by 70% in the same direction as of the previous cold-rolling so as to be of a final gauge of 0.32 mm. When the sheet was annealed in H at a temperature of l,200 C. for 20 hours, there was obtained an excellent double-oriented silicon steel sheet having such magnetic characteristics (Epstein test) as are shown in Table l in the final cold-rolling direction (L) and the direction at a right angle thereto (C). In the Table 1 W 10/50 and W 15/50 (watts per kg.) stand for 1 1 iron core less values when Bm (maximum fiux density) was 10,000 gausses and 15,000 gausses at 50 cycle/ second, respectively and B B B and B stand for magnetic inductions when the magnetizing force was B S 10 and 25 respectively.

TABLE 1 Ba 5 I B40 I 1325 i W 10/50 W /50 Example 2 A 500 kg.-ingot made by melting in an electric furnace and containing 0.080% C., 2.94% Si and 0.026% soluble Al was bloomed in its longitudinal direction to make a slab about 100 mm. thick. The slab was soaked at 1,280 C. for 30 minutes and was then hot-rolled at a reduction rate of about 75% in a direction at a right angle to the longitudinal direction of the slab to make an intermediate slab about 25 mm. thick. The temperature of the slab at that time was 1,050 C. Then the slab was turned by 90 degrees in the direction and was hot-rolled by about 93% so as to be a hot-rolled sheet about 1.6 mm. thick. The finish temperature was about 700 C. The sheet was annealed at 950 C. for 5 minutes. The annealed sheet was pickled and was then cold-rolled at a reduction rate of 70% in the same direction as the final hot-rolling direction so as to be a cold-rolled sheet 0.48 mm. thick. The sheet was decarburized in wet hydrogen at 750 C. for 5 hours (then C:0.003%) and was then annealed in H at a temperature of 1,200 C. for 20 hours. After the annealing, it was found by observing the surface of the specimen by the optical goniometer method that the ratio of substantial (100) [001] orientation recrystallization grains to substantial (100) [011] orientation recrystallization grains was about 1:1 and that their distributions were mixed with each other and were balanced.

When this specimen was cut out in the rolling direction and in the respective directions of 22.5, 45, 67.5 and 90 degrees from the rolling direction respectively and the magnetic characteristics (Epstein test) of each specimen were measured, such results as are shown in Table 2 were obtained.

Example 3 A 500 kg.-ingot of about 250 mm. thick made in an electric furnace and containing 0.045% C, 3.05% Si, 0.030% acid-soluble Al was heated to 1,250 C. and hotrolled in the longitudinal direction of said ingot to make a slab of about mm. thick. The slab was once cooled 12 and then again heated to 1,200 C. The thus reheated slab was hot-rolled in the same direction as the previous hot-rolling direction at the reduction rate of 52% to make a sheet of 12 mm. thick. Thereon, by turning the rolling direction, the hot-rolled sheet was again hot-rolled in the direction at a right angle to the said rolling direction at the reduction rate of thereby a sheet of 3 mm. thick was prepared. The finish temperature was After the hot-rolled sheet was pickled, it was coldrolled in the same direction as the direction of the final hot-rolling stage by 73% and then again cold-rolled in the direction at a right angle to the previous cold-rolling to make a sheet of the final gauge as of 0.3 mm. thick. The final gauge sheet was subjected to the decarburization treatment in wet hydrogen for 5 minutes at a temperature of 800 C. After the decarburized sheet was then annealed in an atmosphere of H for 20 hours at a temperature of 1,200 C., the double-oriented silicon steel sheet having magnetic characteristics (Epstein test) in the final cold-rolling direction and in the direction at a right angle thereto, as are shown in Table 3, was obtained.

What we claim is:

In a process for producing a silicon steel sheet having a (100) plane which comprises hot-rolling a steel ingot, repeating the hot-rolling until a steel sheet 1.0 to 7 mm. thick is obtained, cold-rolling t-he thus-obtained hot-rolled sheet to final gauge, and annealing; the improvement wherein (1) said steel ingot consists essentially of iron, 2 to 4% Si, 0.01 to 0.15% C, and 0.01 to 0.06% acid soluble Al, and (2) said steel ingot is subjected to the second-last hot-rolling in a temperature range of from 800 to 1,250 C. at a reduction rate of from. 30 to 93% and then cross-rolled in a direction at an angle of substantially with the direction of the said second-last hot-rolling, at a reduction rate of from 40 to 97% and in a temperature range of from the temperature at which the second last hot-rolling is finished to 600 C., whereby the carbon content of the steel sheet is retained within the aforesaid range of the carbon content and recrystallization grains having (100) [001] orientation and (100) [011] orientation are produced.

References Cited by the Examiner UNITED STATES PATENTS 2,046,717 7/1936 Bitter 14811l 3,163,564 12/1964 Taguchi et a1. 148l1l 3,164,496 1/1965 Hibbard 148l20 DAVID L. RECK, Primary Examiner.

N, E, MARKVA, Assistant Examiner. 

